(1) Field of the Invention
The present invention relates to a method and system for printing gap adjustment and more particularly to a technique for appropriately adjusting a gap between a print head and a platen in a printing machine such as an impact printer.
(2) Description of the Prior Art
In a printing machine such as an impact printer, a paper sheet is held between a print head and a platen and a pin called "dot pin" strikes the paper sheet from the print head to perform printing in a desirable way. If the gap between the print head and the platen is too narrow in such a printing machine, the pin is more likely to be bent or snapped by the pin striking force and ribbon and paper are also likely to be jammed. On the other hand, too broad a printing gap might cause images to be faint or result in a snap of the pin if strokes exceed a predetermined value. To prevent bending of the pin and an occurrence of ribbon jam or paper jam and to improve print quality, it is necessary to appropriately adjust the printing gap between the print head and platen in accordance with the thickness of a paper sheet to be used.
One known printing gap adjustment system has the structure shown in FIG. 15. In a printing gap adjustment system 100 shown in FIG. 15, there are provided a print head 101 and a platen 102 in opposing relationship. A support shaft 102a of the platen 102 is energized by the spring force of a coil spring 103 in such a direction to separate the shaft 102a from the print head 101 and received by an eccentric cam 104. The eccentric cam 104 is rotated via a link 107 by rotating a lever 105 through a predetermined angle on a supporting point 106, so that the printing gap between the print head 101 and the platen 102 is adjusted. The amount of gap adjustment is checked by reading a gap scale 108 provided on the print head 101. The gap scale 108 is calibrated based on the number of paper sheets overlapped.